1. Technical Field
The invention relates to a semiconductor device and a manufacturing method thereof.
2. Related Art
A trench gate structure in which a gate electrode is formed in a trench has been known as the structure of semiconductor devices (semiconductor elements). Patent Literatures 1 to 4 describe formation of a p-type semiconductor in the vicinity of a bottom of a trench, in order to relieve the potential crowding on the bottom of the trench in the trench gate structure. Patent Literatures 5 to 9 describe formation of a p-type semiconductor as a floating area in a bottom of a trench by using at least either of ion implantation and thermal diffusion, in order to relieve the potential crowding on the bottom of the trench in the trench gate structure. These proposed techniques improve the breakdown voltage of the semiconductor device.    Patent Literature 1: JP H06-224437A    Patent Literature 2: JP 2001-267570A    Patent Literature 3: JP 2009-117593A    Patent Literature 4: JP 2011-44513A    Patent Literature 5: JP H01-310576A    Patent Literature 6: JP H10-98188A    Patent Literature 7: JP 2005-116822A    Patent Literature 8: JP 2007-158275A    Patent Literature 9: JP 2009-267029A